Generally speaking, the conventional analog circuits process signals in the voltage mode, and voltage operational amplifiers (OP Amp) are commonly used by circuit designers due to the low cost and stable technology of the voltage operational amplifiers. However, the conventional voltage operational amplifiers are insufficient in transient response swiftness, which results an limitation on signal-processing design for the circuit designers. To free themselves from such limitation on signal-processing design, the circuit designers usually try to solve this issue by increasing the internal slew rate of the operational amplifiers.
FIG. 1 is a schematic diagram illustrating a conventional operational amplifier. Referring to FIG. 1, a conventional operational amplifier 100 has a feedback configuration. Namely, an output terminal and an inverting input terminal (−) of the operational amplifier 100 are coupled to each other. In this example, when different input voltages Vin are input to a non-inverting input terminal (+) of the operational amplifier 100, the output terminal of the operational amplifier 100 generates different output voltages Vo. FIG. 2 is a waveform diagram illustrating an output voltage of the conventional operational amplifier. Referring to FIG. 2, the operational amplifier 100 is configured to switch the input voltage Vin to the output voltage Vout, wherein a switching rate of the operational amplifier 100 is determined by a ratio (IB/CM) between a bias current (IB) at an input stage of the operational amplifier and an internal compensation capacitance (CM) of the operational amplifier. The ratio is termed as the slew rate SR (i.e. SR=IB/CM). Therefore, if the internal slew rate of the conventional operational amplifiers is to be increased, the bias current at the input stage of the operational amplifier needs to be increased, or the compensation capacitance needs to be reduced.